Java SDK (#3906)

* Java SDK

* update preview config

By using the *repo name* as the key, local `preview` will work naturally
if you have the branch checked out.

(e.g. the previous version would *always* pull the remote URL, and ignore
your local sdk docs checkouts)

---------

Co-authored-by: Hakim Cassimally <[email protected]>

Author: RichardSmedley

preview/HEAD.yml

@@ -25,4 +25,8 @@ sources:
       branches: release/8.0
       start_path: docs
 
-
+  # Minimal SDK build
+    docs-sdk-common:
+      branches: [release/8.0]
+    docs-sdk-java:
+      branches: [3.8-api]